Multiple motor drivers for a hermetically-sealed motor-compressor system

ABSTRACT

A fluid compression system is disclosed having a hermetically-sealed housing with at least two motors and a compressor arranged therein. The motors may be arranged either on both sides of the compressor or in a tandem configuration on one side of the compressor. The motors may be adapted to drive both the compressor and at least one blower device coupled to a free end of shaft that extends through the housing, the blower device being configured to circulate a cooling fluid throughout the housing and thereby cool the motors and any accompanying radial/axial bearings.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application Ser. No. 61/407,148, entitled “Multiple Motor Drivers for a Hermetically-Sealed Motor-Compressor System,” and filed on Oct. 27, 2010. The contents of the priority application are hereby incorporated by reference in their entirety.

BACKGROUND

A motor is often combined with a compressor in a single housing to provide what is known as a motor-compressor device. Via a shared rotating shaft supported on each end by a rotor-bearing system, the motor drives the compressor in order to generate a flow of compressed process gas. When used to drive a compressor, such as a centrifugal compressor, the motor is required to rotate at sufficiently high speeds to facilitate efficient compression of the process gas.

The compression range of the motor-compressor, however, may be limited by the power capacity of the motor driver, which is typically a constant-torque machine. In fact, there are many industrial applications in the field where the compressor power requirements exceed the power capacity of the motor driver. In such instances, the process requirements are often served by multiple motor-compressor arrangements, which can significantly increase the cost, weight, and footprint of the application.

Accordingly, there is a need for an improved motor-compressor arrangement that can supplement the power deficiencies of a single motor driver with a reduced cost when compared to the multiple unit approach.

SUMMARY

Embodiments of the disclosure may include a fluid compression system. The fluid compression system may include a hermetically-sealed housing having a multi-section shaft extending from a first end of the housing to a second end of the housing, a compressor arranged within the housing and including a driven section of the shaft, and a first motor being disposed within the housing axially-adjacent the compressor at the first end, the first motor including a first motor rotor section of the shaft. The fluid compression system may also include a second motor disposed within the housing axially-adjacent the compressor at the second end, the second motor including a second motor rotor section of the shaft, wherein the first and second motor rotor sections are coupled to the driven section at opposing ends such that the motors are configured to simultaneously drive the driven section of the shaft and thereby rotate the compressor.

Embodiments of the disclosure may further provide a method of compressing a fluid. The method may include disposing a first motor, a second motor, and a compressor within a hermetically-sealed housing, the housing having a shaft that extends from a first end of the housing to a second end of the housing, and wherein the first and second motors and the compressor are each coupled to the shaft. The method may further include rotating the shaft with the first motor to provide torque to the shaft and drive the compressor at a first power/torque level, and rotating the shaft with the second motor concurrently with the first motor to provide additional torque to the shaft and drive the compressor at a second power/torque level, wherein the second power/torque level is greater than the first power/torque level.

Embodiments of the disclosure may further provide a fluid compression system. The fluid compression system may include a hermetically-sealed housing having a shaft extending from a first end of the housing to a second end of the housing, a compressor arranged within the housing at the first end and including a driven section of the shaft, and a first motor disposed within the housing at the second end and axially-offset from the compressor, the first motor including a first motor rotor section of the shaft and being in fluid communication with at least one internal cooling passage. The fluid compression system may also include a second motor disposed within the housing interposing the compressor and the first motor, the second motor including a second motor rotor section of the shaft and in fluid communication with at least one internal cooling passage, wherein the first and second motors are configured to drive the driven section of the shaft in tandem and thereby rotate the compressor.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detailed description when read with the accompanying Figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 illustrates an exemplary fluid compression system, according to one or more embodiments disclosed.

FIG. 2 illustrates another exemplary fluid compression system, according to one or more embodiments disclosed.

FIG. 3 illustrates a schematic flow chart of a method for compressing a working fluid, according to one or more embodiments disclosed.

DETAILED DESCRIPTION

It is to be understood that the following disclosure describes several exemplary embodiments for implementing different features, structures, or functions of the invention. Exemplary embodiments of components, arrangements, and configurations are described below to simplify the present disclosure; however, these exemplary embodiments are provided merely as examples and are not intended to limit the scope of the invention. Additionally, the present disclosure may repeat reference numerals and/or letters in the various exemplary embodiments and across the Figures provided herein. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various exemplary embodiments and/or configurations discussed in the various Figures. Moreover, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed interposing the first and second features, such that the first and second features may not be in direct contact. Finally, the exemplary embodiments presented below may be combined in any combination of ways, i.e., any element from one exemplary embodiment may be used in any other exemplary embodiment, without departing from the scope of the disclosure.

Additionally, certain terms are used throughout the following description and claims to refer to particular components. As one skilled in the art will appreciate, various entities may refer to the same component by different names, and as such, the naming convention for the elements described herein is not intended to limit the scope of the invention, unless otherwise specifically defined herein. Further, the naming convention used herein is not intended to distinguish between components that differ in name but not function. Additionally, in the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to.” All numerical values in this disclosure may be exact or approximate values unless otherwise specifically stated. Accordingly, various embodiments of the disclosure may deviate from the numbers, values, and ranges disclosed herein without departing from the intended scope. Furthermore, as it is used in the claims or specification, the term “or” is intended to encompass both exclusive and inclusive cases, i.e., “A or B” is intended to be synonymous with “at least one of A and B,” unless otherwise expressly specified herein.

FIG. 1 illustrates an exemplary fluid compression system 100 according to embodiments described herein. The system 100 includes at least two drivers, such as motors 102 a and 102 b, coupled to a compressor 104 and an integrated separator 106 via a rotatable shaft 108. In the illustrated embodiment, the motors 102 a,b are arranged on opposing axial sides of the compressor 104 and configured to drive the compressor 104 and separator 106 combination. In other embodiments, the separator 106 may be omitted from the system 100 so that motors 102 a,b only drive the compressor 104.

The motors 102 a,b, the compressor 104, and the separator 106 are each positioned within a hermetically-sealed housing 110 having a first end 111 and a second end 113. The housing 110 provides both support and protection for the motors 102 a,b, the compressor 104, and the separator 106 components, such that each component shares the same pressure-containing casing.

The shaft 108 extends substantially the whole length of the housing 110, from the first end 111 to the second end 113, and includes a first motor rotor section 112 a, a second motor rotor section 112 b, and a driven section 114 arranged between the first and second motor rotor sections 112 a,b. As illustrated, the first motor rotor section 112 a of the shaft 108 corresponds to the rotor of the first motor 102 a, and the second motor rotor section 112 b corresponds to the rotor of the second motor 102 b. The driven section 114 of the shaft 108 includes both the compressor 104 and the integrated separator 106. Moreover, the driven section 114 may be connected to the first motor rotor section 112 a via a first coupling 116 a and the second motor rotor section 112 b via a second coupling 116 b, such that when the first and second rotor sections 112 a,b rotate, they drive the driven section 114. The first and second couplings 116 a,b may be any type of shaft 108 coupling known to those skilled in the art, and may include a flexible or a rigid coupling. The first and second couplings 116 a,b may be disposed within corresponding first and second cavities 115 a and 115 b, respectively, defined within the housing 110.

In operation, the motors 102 a,b work together to rotate the compressor 104 (and the separator 106, if used) providing more power and torque than could be achieved with the use of a single motor. Because the amount of power delivered by each motor 102 a,b is inherently limited, the use of two motors in series allows an increase in the power capability and capacity of the overall fluid compression system 100 or motor/compressor arrangement, which allows an extension of the process capabilities that can be met by the compressor 114.

Each motor 102 a,b may be a permanent magnet-type electric motor, having permanent magnets 117 on the rotor and having a stator 118, or an induction-type machine with a squirrel cage mounted on the rotor (117) and having a stator 118. As will be appreciated, other types of motors 102 may be used, such as, but not limited to, synchronous, brushed DC motors, etc.

The motor rotor sections 112 a,b and driven section 114 of the shaft 108 are supported at or near each end, respectively, by one or more radial bearings 120. Each radial bearing 120 are directly or indirectly supported by the housing 110, and in turn provide rotational support to the motor rotor sections 112 a,b and driven section 114. In one embodiment, the bearings 120 may be magnetic bearings, such as active or passive magnetic bearings. In other embodiments, however, other types of bearings 120 may be used. In addition, at least one axial thrust bearing 122 may be arranged on the shaft 108 between the compressor 104 and the first motor 102 a. In other embodiments, the axial thrust bearing 122 may be arranged outboard from the first motor 102 a, at or near the end of the shaft 108 adjacent the first end 111 of the housing 110. The axial thrust bearing 122 may be a magnetic bearing and be configured to at least partially bear axial thrusts generated by the compressor 104.

The compressor 104 may be a multi-stage centrifugal compressor with one or more, in this case three, compressor stages or impellers 124. As can be appreciated, however, any number of impellers 124 may be implemented or used without departing from the scope of the disclosure. The separator 106 separates and removes higher-density components from lower-density components contained within a process gas introduced into the system 100. Any higher-density components removed from the process gas are discharged from the separator 106 via a discharge line 126, thereby providing a relatively dry process gas to the succeeding compressor 104. Especially in subsea applications where the process gas is commonly multiphase, any separated liquids discharged via line 126 may accumulate in a collection vessel (not shown) and be subsequently pumped back into the process gas at a downstream pipeline location (not shown). Otherwise, separated liquids may be drained into said collection vessel and disposed of properly, as known in the art.

A balance piston 125, including an accompanying balance piston seal 127, may be arranged on the shaft 108 between the compressor and the second motor 102 b. Due to the pressure rise developed through the compressor 104, a pressure difference is created such that the compressor 104 has a net axial thrust in the direction of its inlet. The balance piston 125 serves to counteract that force, and any compressor 104 thrust not absorbed by the balance piston 125 may be otherwise absorbed by the thrust bearing(s) 122.

Still referring to FIG. 1, the system 100 further includes a closed-loop cooling system configured to regulate the temperature of the motors 102 a,b and bearings 120, 122 during operation of the system 100. In one embodiment, the closed-loop cooling system includes a first blower device 128 a disposed at or near a free end 134 a of the first motor rotor section 112 a, located outboard from the first motor 102 a, and a second blower device 128 b disposed at or near a free end 134 b of the second motor rotor section 112 b, located outboard from the second motor 102 b. Each blower device 128 a,b includes an impeller, such as a first impeller 130 a and a second impeller 130 b, respectively, disposed within the housing 110 and configured to generate head pressure required to circulate cooling fluid through the closed-loop cooling circuit described below. In at least one embodiment, each impeller 130 a,b may be a centrifugal compression impeller and may be mounted on or otherwise attached to the respective free ends 134 a,b of the motor rotor sections 112 a,b of the shaft 108. Consequently, rotation of the shaft 108 will also drive each impeller 130 a,b and thereby draw cooling fluid into each blower device 128 a,b to be compressed and circulated throughout the closed-loop cooling circuit.

In one or more embodiments, the closed-loop cooling system may include only the first blower device 128 a or otherwise include only the second blower device 128 b, without departing from the scope of the disclosure. In other embodiments, the closed-loop cooling system may include a single blower device (not shown) coupled to the exterior of either the first end 111 or the second end 113 of the housing 110. In said embodiment, the impeller of the single blower device may be mounted on or otherwise attached to the free end 134 a or 134 b of the shaft 108 as it extends through the first end 111 or second end 113, respectively. Such an embodiment is discussed in detail in co-pending U.S. Pat. App. No. 61/407,059 (Atty. Dock. # 42495.600) entitled “Method and System for Cooling a Motor-Compressor with a Closed-Loop Cooling Circuit,” and filed on Oct. 27, 2010, the contents of which are hereby incorporated by reference to the extent consistent with the present disclosure.

In operation, a process gas to be compressed or otherwise treated is introduced into the system 100 via an inlet 142. The process gas may include, but is not limited to, a hydrocarbon gas, such as a mixture of natural gas or methane derived from a production field or via a pressurized pipeline. In other embodiments, the process gas may include air, CO₂, N₂, ethane, propane, i-C₄, n-C₄, i-C₅, n-C₅, and/or combinations thereof.

In at least one embodiment, especially in subsea oil and gas applications, the process gas may be a “wet” process gas having both liquid and gaseous components, or otherwise including a mixture of higher-density and lower-density components. Accordingly, the separator 106 receives the process gas via the inlet 142 and removes portions of high-density components therefrom, thereby generating a substantially dry process gas. The liquid and/or higher-density components extracted from the process gas by the separator 106 are removed via the discharge line 126, as described above. The compressor 104 receives the substantially dry process gas from the separator 106 and compresses the dry gas through the successive stages of impellers 124 to thereby produce a compressed process gas that is ejected from the compressor 104 via a process discharge 144.

To contain the process gas within the housing 110 and prevent “dirty” process gas from leaking into the adjacent bearing assemblies 120, 122, the closed-loop cooling circuit, and motors 102 a,b, the system 100 includes one or more buffer seals 146. The buffer seals 146 may be radial seals arranged at or near each end of the driven section 114 of the shaft 108 and inboard of the bearings 120.

In one or more embodiments, the buffer seals 146 may be brush seals or labyrinth seals. In other embodiments, the buffer seals 146 may be dry gas seals or carbon ring seals configured to receive a feed of pressurized seal gas via lines 148. When compared to conventional labyrinth or brush seals, the use of carbon rings buffer seals 146 may significantly reduce the amount of seal gas that is consumed, thereby increasing compressor performance efficiency. Moreover, carbon ring seals are less expensive and less susceptible to damage than conventional dry gas seal assemblies, especially when processing wet process gases. Appropriate implementation of carbon ring seals as buffer seals 146 in the system 100 is also described in co-pending U.S. Pat. App. No. 61/407,059 (42495.600), indicated above as being incorporated by reference.

The seal gas in lines 148 is a pressurized process gas that may be derived from the discharge 144 of the compressor 104 and filtered for injection into the buffer seals 146. In other embodiments, however, especially in applications having dry gas seals as buffer seals 146, the seal gas in lines 148 may be a source of clean hydrocarbon gas, hydrogen, or inert gases such as helium, nitrogen, or CO₂. During operation of the system 100, the seal gas creates a pressure differential designed to prevent process gas leakage across the buffer seals 146 and into locations of the housing 110 where the bearings 120, 122 and the motors 102 a,b are located.

In order to cool or otherwise regulate the temperature of the motors 102 a,b and the bearings 120, 122 during operation, cooling fluid is circulated throughout the housing 110 in a cooling loop, or closed-loop cooling circuit, powered by at least one of the blower devices 128 a,b. The blower devices 128 a,b immerse the motors 102 a,b and accompanying bearings 120,122 in an atmosphere of pressurized cooling fluid. In one or more embodiments, the cooling fluid may be the same as the seal gas in lines 148. In other embodiments, the cooling fluid, seal gas, and process gas may all be the same fluid, which may prove advantageous in maintaining and designing any auxiliary systems.

Since each impeller 130 a,b may be directly coupled to a corresponding rotor section 112 a,b, each impeller 130 a,b operates as long as at least one motor 102 a,b is in operation and driving the shaft 108. As each impeller 130 a,b rotates, it draws in cooling fluid, compresses it, and ultimately ejects the cooling fluid via respective outlets 140 a or 140 b and into lines 154 a or 154 b, respectively. Valves 153 a and 153 b may be communicably coupled to lines 154 a,b, respectively, to regulate or otherwise control the head pressure of the cooling fluid as the system 100 reaches its normal operating speed. In other embodiments, one or both of the valves 153 a,b may be entirely omitted from the system 100 and the cooling fluid may instead be circulated at a pressure proportional to the rotational speed of the shaft 108 and the existing flow resistance within the cooling loop.

In at least one embodiment, the cooling fluid in lines 154 a,b may be directed through respective heat exchangers 156 a and 156 b adapted to reduce the temperature of the cooling fluid, and also directed to respective gas conditioning skids 157 a and 157 b configured to filter the cooling fluid. In one embodiment, the heat exchangers 156 a,b are a single heat exchanger fluidly coupled to both lines 154 a,b, and the gas conditioning skids 157 a,b are a single gas conditioning skid also fluidly coupled to both lines 154 a,b. In one embodiment, the gas conditioning skids 157 a,b and/or the heat exchangers 156 a,b may include a density-based separator (not shown), or the like, configured to remove any condensation generated by reducing the temperature of the cooling fluid.

Other embodiments contemplated herein include placing the heat exchangers 156 a,b and accompanying gas conditioning skids 157 a,b prior to the blower devices 128 a,b. As can be appreciated, cooling and conditioning the cooling fluid prior to entering the blower devices 128 a,b may prove advantageous, since a lower-temperature working fluid will demand less power from the motors 102 a,b to compress and circulate the cooling fluid.

At least one external gas conditioning skid 159 may also be included in the system 100 and configured to provide the seal gas for the buffer seals 146 via lines 148 during system 100 start-up and during normal operation. During start-up there may exist a pressure differential between the area surrounding the compressor 104 and the area surrounding each motor 102 a,b. The seal gas entering the buffer seals 146 may leak into the area surrounding the motors 102 a,b until reaching the desired suction pressure of the compressor 104. The external conditioning skid 159 may also provide initial fill gas via line 164 to provide pressurized cooling fluid for the system 100 until an adequately pressurized source of process gas/cooling fluid may be obtained from the discharge 144 of the compressor 104. Accordingly, the initial fill gas may be cooling fluid or process gas added to the system 100. During normal operation, fill gas from line 164 may also be used in the event there is a sudden change in pressure in the system 100 and pressure equilibrium between the compressor 104 and the motor 102 must be located in order to stabilize the cooling loop.

The cooled and filtered cooling fluid is discharged from the first gas conditioning skid 157 a and into line 158 a. Line 158 a is subsequently separated into lines 160 and 162 before injecting the cooling fluid into internal cooling passages 150 a and 150 b, respectively, defined within the housing 110 and configured to cool the first motor 102 a and bearings 120 that support the first motor rotor section 112 a. As the cooling fluid circulates around the first motor 102 a and passes through the adjacent bearings 120 (i.e., through a gap formed between each bearing 120 and the shaft 108), heat is drawn away from the first motor 102 a and each adjacent bearing 120. The cooling fluid returns or otherwise loops back to the first impeller 130 a either by passing through the bearings 120 outboard from the first motor 102 a, or by passing through the bearings 120 inboard of the first motor 102 a and into the first cavity 115 a where it circulates through a first return line 166 a fluidly coupled to the first impeller 130 a.

On the other side of the system 100, cooled and filtered cooling fluid is discharged from the second gas conditioning skid 157 b and into line 158 b. Line 158 b is subsequently separated into lines 168 and 170, where line 168 is split and introduced into internal cooling passages 152 a and 152 b defined within the housing 110 to cool the bearings 120, 122 that support the driven section 114 of the shaft 108. As the cooling fluid nears the bearings 120, the buffer seals 146 generally prevent the cooling fluid from passing into the separator 106 and/or compressor 104. Instead, the cooling fluid freely passes through the bearings 120 toward the ends of the driven section 114, simultaneously drawing heat away from the bearings 120. As can be appreciated, there may be embodiments where at least a small portion of the seal gas in lines 148 provided to the buffer seals 146 may be combined with the cooling fluid at each end of the driven section 114 of the shaft 108.

The cooling fluid coursing through the internal cooling passage 152 a may also be configured to cool the axial thrust bearing 122 as it channels toward the first coupling 116 a and is ultimately discharged into the first cavity 115 a. The cooling fluid coursing through internal cooling passage 152 b may cool the bearings 120 adjacent the second coupling 116 b and in due course escape into the second cavity 115 b.

The cooling fluid in line 170 may be split or otherwise introduced into internal cooling passages 152 c and 152 d defined within the housing 110 to cool the second motor 102 b and adjacent bearings 120 that provide support to the second motor rotor section 112 b. As the cooling fluid circulates around the second motor 102 b and passes through the adjacent bearings 120 on each side, heat is drawn away to cool the first motor 102 b and each adjacent bearings 120. The cooling fluid returns or otherwise loops back to the second impeller 130 b either by passing through the bearings 120 outboard from the second motor 102 b, or by passing through the bearings 120 inboard of the second motor 102 b and into the second cavity 115 b where it circulates through a second return line 166 b fluidly coupled to the second impeller 130 b.

The system 100 may further include a first pressure balance line 172 a fluidly coupled to both the first return line 166 a and the first end 111 of the housing 110, and a second pressure balance line 172 b fluidly coupled to both the second return line 166 b and the second end 113 of the housing 110. The pressure balance lines 172 a,b counteract or otherwise equalize axial forces generated by the respective impellers 130 a,b. A third pressure balance line 172 c may fluidly connect the first and second cavities 115 a,b so as to maintain a substantially constant cooling fluid pressure between the first impeller 130 a and the second impeller 130 b. It should be noted here again that, although not shown, the cooling loops for both motors 102 a,b may be combined into a single cooling loop system that uses only one cooler and one gas conditioning skid or system.

The embodiments described herein are advantageous for a variety of reasons. For example, since the system 100 employs two motors 102 a,b within the same hermetically-sealed housing 100, the power and torque capability of the system 100 is dramatically increased. Furthermore, the system 100 may prove advantageous in motor-compressor applications having a laminated shaft 108, as opposed to a solid shaft 108 design. Laminated shafts for high-speed motors are generally not designed to work in a drive-through configuration which would require one motor to deliver increased amounts of torque to a single end of the compressor 104, and would probably otherwise fail under such an increase in power. Instead, the system 100 as described delivers torque to the compressor 104 from both ends of the compressor 104 via the first and second motors 102 a,b, thereby dividing the torque input to separated portions of the shaft 108.

Referring now to FIG. 2, depicted is another exemplary fluid compression system 200, similar in some respects to the fluid compression system 100 described above in FIG. 1. Accordingly, the system 200 may be best understood with reference to FIG. 1, where like numerals correspond to like components that will not be described again in detail. Similar to the system 100 of FIG. 1, the system 200 may include at least two prime movers, such as motors 102 a and 102 b, coupled to the compressor 104 and the separator 106 via the rotatable shaft 108. The motors 102 a,b, the compressor 104, and the separator 106 are each positioned within the hermetically-sealed housing 110 having a first end 111 and a second end 113.

The motors 102 a,b in system 200 are arranged in tandem and power the compressor 104 and separator 106 from a single side of the compressor 104. The first motor 102 a and its accompanying bearings 120 and blower device 128 a are arranged on the outboard side of the second motor 102 b. The shaft 108 may again include first and second motor rotor sections 112 a,b and a driven section 114. However, it is only the second motor rotor section 112 b that is coupled to the driven section 114 of the shaft 108 via the second coupling 116 b, whereas the first motor rotor section 112 a is coupled to the opposing end of the second motor rotor section 112 b via the first coupling 116 a. As will be appreciated, the tandem arrangement of the motors 102 a,b may be disposed on either side of the compressor 104 without departing from the scope of the disclosure.

The closed-loop cooling system of FIG. 2 may be substantially similar to the closed-loop cooling system of FIG. 1. For example, cooling fluid in lines 160 and 162 is injected into internal cooling passages 150 a and 150 b, respectively to cool the first motor 102 a and the bearings 120 that support the first motor rotor section 112 a of the shaft 108. Moreover, the cooling fluid in line 170 is split and injected into internal cooling passages 152 c,d to cool the second motor 102 b and the bearings 120 that support the second motor rotor section 112 b of the shaft 108. It will be further appreciated that the closed-loop cooling system of FIG. 2 may omit either the first or the second blower device 128 a,b without departing from the scope of the disclosure. In other embodiments, the closed-loop cooling system may include a single blower device (not shown) coupled to the exterior of the second end 113 of the housing 110, such as is disclosed in co-pending U.S. Pat. App. No. 61/407,059 (Atty. Dock # 42495.600), indicated above as being incorporated by reference.

The cooling fluid in line 168 is split and introduced into the internal cooling passages 152 a,b to cool the bearings 120 that support the driven section 114 of the shaft 108. The cooling fluid in the internal cooling passage 152 a may also cool the axial thrust bearing 122 as it channels toward the compressor end 111 of the housing 110 and is ultimately discharged via line 174. The cooling fluid in the internal cooling passage 152 b may escape into the second cavity 115 b. In one embodiment, the second cavity 115 b may also receive cooling fluid via line 174. Accordingly, the cooling fluid channeled through the internal cooling passages 152 a,b is combined or otherwise mixed within the second cavity 115 b.

Cooling fluid collected in the first and second cavities 115 a,b is discharged into a return line 176 fluidly coupled to each cavity 115 a,b. The return line 176 recycles a portion of the cooling fluid back to each impeller 130 a,b to thereby start the closed-loop cooling circuit over again. A balance line 178 may be fluidly coupled to the return line 176 and the motor end 113 of the housing 110 and to counteract or otherwise equalize axial forces generated by the impellers 130 a,b.

Several variations of the system 200 may be undertaken without departing from the scope of the disclosure. For example, as described above, the first and second heat exchangers 156 a,b may be a single heat exchanger, and the first and second gas conditioning skids 157 a,b may be a single gas conditioning skid. Also, the first or the second heat exchanger 156 a,b may be disposed before the blower devices 128 a,b so as to decrease the temperature of the recycled cooling fluid before recompression in each impeller 130 a,b. Furthermore, the separator 106 may be omitted from the system 200 so that the motors 102 a,b only drive the compressor 104.

Referring now to FIG. 3, illustrated is a flowchart depicting an exemplary method 300 of compressing a fluid. The method 300 may include arranging first and second motors and a compressor within a hermetically-sealed housing or casing, as at 302. The housing may have a shaft that extends from a first end to a second end of the housing. Each of the first and second motors and the compressor may be coupled to the shaft such that rotation of at least one of the motors necessarily drives the compressor and compresses the fluid. In one embodiment, the first and second motors are arranged within the housing on opposing sides of the compressor. In another embodiment, the first and second motors are arranged in tandem and axially-spaced from the compressor along the shaft. In at least one embodiment, a separator is also disposed within the housing, axially-spaced from the compressor.

The method 300 may also include rotating the shaft with the first motor to drive the compressor at a first power/torque level, as at 304. In an embodiment, the first power/torque level is proportional to the power capability and/or maximum torque that can be provided by the first motor when taking into account the mass of the compressor (and potentially the separator if employed), the work of compression, and any other frictional drag forces that must be overcome to rotate the shaft. The method 300 may further include rotating the shaft with the second motor to drive the compressor at a second or higher power/torque level, as at 306, wherein the second power/torque level is greater than the first power/torque level and greater than a power/torque level that could be achieved by a single motor. As can be appreciated, the addition of the second motor may provide supplementary torque to the shaft to complement the power capability of the first motor. Consequently, the compressor can handle more demanding power conditions than what the first motor alone could supply, thereby increasing the overall compression power of the motor-compressor system.

The method 300 may further include supporting the shaft within the housing with a plurality of radial bearings, as at 308. As the shaft rotates, a first impeller coupled to a first free end of the shaft rotates and circulates a cooling fluid throughout the housing to cool the first and second motors and the bearings, as at 310. In one or more embodiments, the housing may define a plurality of internal cooling passages that are in fluid communication with the plurality of radial bearings and the first and second motors. As the cooling fluid circulates through the internal cooling passages, heat is drawn away from the motors and bearings, thereby cooling or otherwise regulating the temperature of said components. The cooling fluid is then returned to the first impeller, as at 312, thereby completing a closed-loop cooling circuit. Accordingly, after cooling the internal components, the cooling fluid is recycled back to the impeller to be recompressed and recirculated back through the housing. In embodiments including an axial thrust bearing also disposed about the shaft, the cooling fluid may be configured to remove heat therefrom also.

The foregoing has outlined features of several embodiments so that those skilled in the art may better understand the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure. 

1. A fluid compression system, comprising: a hermetically-sealed housing having a multi-section shaft extending from a first end of the housing to a second end of the housing; a compressor arranged within the housing and including a driven section of the shaft; a first motor being disposed within the housing axially-adjacent the compressor at the first end, the first motor including a first motor rotor section of the shaft; a second motor disposed within the housing axially-adjacent the compressor at the second end, the second motor including a second motor rotor section of the shaft, wherein the first and second motor rotor sections are coupled to the driven section at opposing ends such that the motors are configured to simultaneously drive the driven section of the shaft and thereby rotate the compressor; radial bearings disposed proximal each end of the first and second motor rotor sections and each end of the driven section, the radial bearings being in fluid communication with at least one internal cooling passage defined within the housing; and a first impeller coupled to a free end of the second motor rotor section of the shaft, whereby rotation of the second motor rotor section drives the first impeller and circulates a cooling fluid in a closed cooling loop through internal cooling passages defined within the housing.
 2. (canceled)
 3. The fluid compression system of claim 1, further comprising a second impeller coupled to a free end of the first motor rotor section of the shaft, whereby rotation of the first motor rotor section drives the second impeller and circulates the cooling fluid in the closed cooling loop through the internal cooling passages.
 4. The fluid compression system of claim 1, wherein the radial bearings are magnetic bearings.
 5. The fluid compression system of claim 1, further comprising a separator axially-spaced from the compressor and disposed within the housing, the separator being coupled to the driven section of the shaft.
 6. The fluid compression system of claim 1, wherein the first motor rotor section and the driven section are connected via a first coupling.
 7. The fluid compression system of claim 6, wherein the second motor rotor section and the driven section are connected via a second coupling.
 8. The fluid compression system of claim 1, wherein the compressor is a multi-stage centrifugal compressor.
 9. A method of compressing a fluid, comprising: disposing a first motor, a second motor, and a compressor within a hermetically-sealed housing, the housing having a shaft that extends from a first end of the housing to a second end of the housing, and wherein the first and second motors and the compressor are each coupled to the shaft; rotating the shaft with the first motor to provide torque to the shaft and drive the compressor at a first power/torque level; and rotating the shaft with the second motor concurrently with the first motor to provide additional torque to the shaft and drive the compressor at a second power/torque level, wherein the second power/torque level is greater than the first power/torque level.
 10. The method of claim 9, further comprising: supporting the shaft within the housing with a plurality of radial bearings, the housing defining a plurality of internal cooling passages in fluid communication with the plurality of radial bearings and the first and second motors; driving a first impeller coupled to a first free end of the shaft; circulating a cooling fluid through at least one of the internal cooling passages of the housing with the first impeller; cooling the first and second motors and the plurality radial bearings with the cooling fluid; and returning the cooling fluid to the impeller in a closed-loop circuit.
 11. The method of claim 10, further comprising: driving a second impeller coupled to a second free end of the shaft; circulating the cooling fluid through at least one of the internal cooling passages of the housing with the second impeller; cooling the first and second motors and the plurality radial bearings with the cooling fluid; and returning the cooling fluid to the second impeller in the closed-loop circuit.
 12. The method of claim 11, further comprising directing the cooling fluid through a heat exchanger to reduce the temperature of the cooling fluid.
 13. The method of claim 12, further comprising filtering the cooling fluid with a gas conditioning skid.
 14. The method of claim 10, further comprising cooling an axial thrust bearing with the cooling fluid, the axial thrust bearing being disposed on the shaft between the compressor and the first motor.
 15. The method of claim 10, further comprising separating high-density components from low-density components in the fluid with an integrated separator arranged within the housing and axially-spaced from the compressor, the integrated separator being coupled to the shaft such that rotation of the shaft drives the integrated separator.
 16. A fluid compression system, comprising: a hermetically-sealed housing having a shaft extending from a first end of the housing to a second end of the housing; a compressor arranged within the housing at the first end and including a driven section of the shaft; a first motor disposed within the housing at the second end and axially-offset from the compressor, the first motor including a first motor rotor section of the shaft and being in fluid communication with at least one internal cooling passage; a second motor disposed within the housing interposing the compressor and the first motor, the second motor including a second motor rotor section of the shaft and being in fluid communication with at least one internal cooling passage, wherein the first and second motors are configured to drive the driven section of the shaft in tandem and thereby rotate the compressor; radial bearings disposed proximal each end of the first and second motor rotor sections and each end of the driven section, the radial bearings being in fluid communication with at least one internal cooling passage; and a first impeller coupled to a free end of the first motor rotor section of the shaft, whereby rotation of the first motor rotor section drives the first impeller and circulates a cooling fluid in a closed cooling loop through the internal cooling passages.
 17. The fluid compression system of claim 16, further comprising: a first coupling connecting the first motor rotor section to the second motor rotor section; and a second coupling connecting the second motor rotor section to the driven section.
 18. (canceled)
 19. The fluid compression system of claim 16, further comprising a second impeller coupled to the second motor rotor section of the shaft and disposed between the first and second motors, whereby rotation of the second motor rotor section drives the second impeller and circulates the cooling fluid in the closed cooling loop through the internal cooling passages.
 20. The fluid compression system of claim 16, further comprising a separator axially-spaced from the compressor and disposed within the housing, the separator being coupled to the driven section of the shaft. 21-30. (canceled)
 31. The method of claim 12, further comprising filtering the cooling fluid with a gas conditioning skid. 32-37. (canceled) 